1. Field of the Invention
This invention relates to a substrate-stacking structure suited for use, for example, in an electronic control unit (ECU) in which a substrate, having heat-generating parts mounted thereon, and a control substrate, having control parts mounted thereon, are held spaced a predetermined distance from each other.
2. Related Art
One such substrate-stacking structure of this type is disclosed in JP-A-6-45371U, and is shown in FIG. 20. As shown in FIG. 20, this substrate-stacking structure includes a casing 1 having a terminal holder 2 provided at a lower portion thereof. A printed circuit substrate 4, having a relay 3 (which is a heat-generating part for a large electric current) mounted thereon, is provided at that side of the casing 1 where the terminal holder 2 is provided. A control substrate 7, having control parts 5 and 6, such as an IC and a transistor, is provided at an upper portion of the casing 1 in opposed relation to the relay 3. The printed circuit substrate 4 and the control substrate 7 are disposed in stacked, opposed relation to each other within the casing 1, and are spaced a predetermined distance from each other.
In the above conventional substrate-stacking structure, however, the control substrate 7, having the control parts 5 and 6 mounted thereon, is disposed in opposed relation to the relay 3 mounted on the printed circuit substrate 4, and therefore the control parts 5 and 6 and the control substrate 7 have been liable to be influenced by radiation heat from the relay 3 and the printed circuit substrate 4.
Therefore, this invention has been made in order to solve the above problem, and an object of the invention is to provide a substrate-stacking structure in which the influence of radiation heat, generated from a heat-generating part and a printed circuit substrate, on control parts and a control substrate, can be reduced.
According to the invention, there is provided a substrate-stacking structure comprising: a main substrate as first substrate having a heat-generating part mounted thereon; a control substrate as second substrate having a control part mounted thereon; and a heat shielding plate is interposed between the first and second substrates; wherein the first substrate and the second substrate are held spaced a predetermined distance from each other through a holding plate.
In this substrate-stacking structure, radiation heat from the heat-generating part and the main substrate is intercepted by the heat shielding plate, and therefore the control part and the second substrate will not be influenced by the radiation heat.
The substrate-stacking structure of the invention is further characterized in that the heat shielding plate is formed integrally with the holding plate, and an air layer is formed between the heat shielding plate and the second substrate.
In this substrate-stacking structure, the air layer is positively formed between the heat shielding plate and the control substrate through the holding plate, and the radiation heat from the heat-generating part and the substrate can be efficiently radiated through the heat shielding plate and the air layer.
The substrate-stacking structure of the invention is further characterized in that the holding plate includes a side wall portion from which a hook portion is projected and the heat shielding plate is formed integrally with the holding plate, and wherein the hook portion is engaged in a recess formed on the second substrate, so that the second substrate is positioned in relative to the first substrate.
In this substrate-stacking structure, the second substrate as control substrate is reliably positioned in relative to the first substrate as main substrate.
The substrate-stacking structure of the invention is further characterized in that at least one projection is formed on the heat shielding plate, and the projection abuts with the second substrate, so that the air layer between the heat shielding plate and the control substrate is always kept to a constant value.
In this substrate-stacking structure the air layer between the heat shielding plate and the control substrate is always kept to a constant value through the projections formed on the heat shielding plate.